This invention relates to dental syringe assemblies such as are used by dentists to direct air and/or water into a patients mouth for cleansing and drying purposes.
An assembly of this kind is described in prior patent specification WO 90/07912. The assembly described has a disposable plastics syringe tip which is connected via an adaptor to a handpiece body to which air and water are supplied. The tip can be discarded after use to avoid spread of infection between patients. The adaptor is selected for the particular handpiece body to permit use of a tip having a standardised connection. It is also possible to connect a disposable plastics syringe tip directly (i.e. without an adaptor) to a dedicated handpiece body.
Whilst this known arrangement provides an effective means of preventing transfer of infection via material retained within the tip, there is the possibility of infected material from one patient gaining access beyond the tip to the handpiece body or adaptor from where it can be passed on to the next patient through a fresh tip.
With a view to overcoming this problem, prior application PCT/GB 98/01754 proposes the provision of a non-return valve between the tip and the hand-piece body. This can prevent flow-back of infected material but, in the case where the valve is provided in the handpiece body there is the-problem of conveniently sterilising the valve itself.
An object of the present invention is to provide an improved handpiece having means to avoid transfer of infection due to access of infected material beyond the tip and which is convenient to sterilise.
According to one aspect of the invention therefore there is provided a handpiece for a dental syringe assembly adapted to be connected on the one hand to sources of air and water, and on the other hand to a tip for directing flow of air and water from the handpiece into a patient""s mouth, characterised in that the handpiece is comprised of at least two releasably connectable members, and wherein one of said handpiece members has a non-return valve incorporated therein.
With this arrangement, the valve can help prevent draw back along the tip from the open end thereof of contaminated fluids and can also block access of infected material beyond the tip and thereby prevent transmission of infection between patients.
In addition, in so far as the handpiece members are separable cleansing and sterilisation can be effected in a particularly convenient manner, a consideration which is of upmost importance when providing instruments for dental treatment.
The separable members of the handpiece may comprise a head member which is adapted to be connected to the tip and a body member which is adapted to be connected to the air and water sources, the head member incorporating the non-return valve.
The body member may house a coupling or connecting member with conduits to channel the flow of air and water through the body to the head member. The conduits may be provided with shut off valves.
The body member may comprise a tubular structure which is screwed or otherwise releasably engaged relative to the head member. Where the aforesaid connecting member is provided the head member may be held in detachable engagement with the connecting member by the said releasable engagement of the tubular structure with the head member.
In the case where the syringe assembly is arranged for separate delivery of air and water, the non-return valve is preferably applied to the water delivery, although alternatively or additionally, the valve may be applied to the air delivery.
In a particularly preferred embodiment, the tip has separate air and water passages which may be arranged coaxially or alongside each other and these are connected separately to air and water inlets at the handpiece body, and in this case the non return valve is preferably applied to the water passage only.
The non-return valve may be of any suitable form. In a preferred embodiment, the valve has a spring loaded valve member, such as a ball, which is urged into sealing engagement with a valve seat, fluid pressure during normal operation being sufficient to move the member off the seat to permit passage of fluid.
Other kinds of non-return valve can also be used. For example, in an alternative embodiment, the valve is of the constriction kind whereby valve parts, such as silicon rubber reeds, tend to collapse or are urged into sealing contact with each other but move apart in normal operation to permit passage of fluid.
In the case where the valve is applied to water delivery which is separated from air delivery, the valve may incorporate an outlet flow nozzle to direct flow into the water passage of the tip and help prevent communication, and hence transfer of material, between the air and water passages.
This nozzle may be such as to extend into the water passage of the tip and help form a seal therewith. The nozzle may be tapered to form a tight wedging fit within the tip passage and this may contribute to or establish a seal. Alternatively or additionally there may be an O-ring seal or other sealing arrangement to fit around the tip passage, for example an O-ring seal concentrically around the said nozzle whereby a tubular part of the tip defining an inlet to the water passage fits tightly between the nozzle and the O-ring seal.
As described in the above mentioned prior patent specification, the tip may be disposable and the handpiece may be adapted for detachable engagement for use with a standardised tip directly or via an adapter.
The handpiece may be adapted for detachable engagement with the tip via a bayonet connection, although other connections may also be used.
In a particularly preferred embodiment the handpiece incorporates a sleeve structure for detachable engagement with the tip, preferably via the aforesaid bayonet connection, and this sleeve structure preferably incorporates the said non-return valve and preferably also is incorporated in the aforesaid head member.
This sleeve structure may be located in a bore in the handpiece so as to be movable axially inwardly of the handpiece against the action of a spring to facilitate the aforesaid detachable interengagement. The sleeve structure, and hence the tip when connected thereto, may be rotatable when the sleeve structure is spring urged to an outer limit position whereas rotation may be resisted when the sleeve structure is pushed against the spring to an inner limit position. An appropriate toothed clutch or other mechanism or device may be provided to achieve this resistance. The resistance to rotation enables interengagement and disengagement of the tip and sleeve structure whilst free rotation, preferably through 360xc2x0, facilitates easy use of the tip. Connections of air and water to the tip preferably occur via the sleeve structure preferably such as to maintain flow during such rotation.
The above described sleeve structure advantageously provides a convenient means of attachment of a tip of the kind having a connection cap direct to a handpiece preferably using a bayonet connection.
Thus and in accordance with a further aspect of the present invention there is provided a dental syringe assembly comprising a handpiece adapted to be connected to sources of air and water and a tip for directing flow of air and water from the handpiece into a patients mouth, the tip having an enlarged connector cap at a rear end, and the handpiece having a body member and a head member, characterised in that the head member is provided with a sleeve structure and the connector cap of the tip is detachably interengageable with the sleeve structure.
Other aspects of the sleeve structure and the tip may be as described above.
The head member may be connected to the body member so as to be separable therefrom.
Preferably, the body member comprise a tubular structure which is releasably connected to the head member. Preferably also the body member houses a tubular structure which is releasably connected to the head member.
In a particularly preferred embodiment, the said sleeve structure is provided in a connection piece attached to the head member.
Preferably, the tip has inner and outer coaxial passages for the water and air flow and the said sleeve structure comprises a central inner bore to communicate with the inner coaxial passage within the cap, and an outer passageway defined by a recess around the inner bore to communicate with the outer coaxial passage within the cap.
Preferably also, the connection piece is attached to the head member within a socket of the head member, whereby air and water passageways in the head member are in sealed communication respectively with air and water passageways on the connection piece.
The connection piece preferably has a head part which projects externally of the head member of the handpiece, the sleeve structure being provided exclusively within this head part.
Further, the connection piece is preferably located within the socket so as to be rotatable about its axis whilst being retained against axial separation. The connection piece may be retained by a transverse assembly pin passed through the head member and engaging a peripheral groove in the connection piece.